Nutrition and the Digestive System
The Liver
- The liver is the largest organ of the body. It is
divided- into a right and a left lobe. The functional
units of the liver are called lobules.^
- The functions of the liver are so numerous and
important that we cannot live without it. It produces
heparin, prothrombin, and thrombin. Its Kupffer cells
phagocytose bacteria and worn-out blood cells. It
stores excess carbohydrates as glycogen.^
It stores copper, iron, and vitamins A, D, E, and K.
It stores or transforms poisons into less harmful
substances. It produces bile salts that emulsify or
break down fats.^
- The gallbladder stores and concentrates bile
produced by the liver lobules. The bile enters the
duodenum of the small intestine through the
common bile duct.
The Small Intestine
- The main function of the small intestine is the
completion of absorption of the digested food. It
is divided into three portions: the duodenum (10
inches), the jejunum (8 feet), and the ileum (12
feet). The ileocecal valve connects the small
intestine with the large intestine.^
- In addition to its length, the walls of the small
intestine are thrown into folds called plicae that are
covered with millions of villi. Nutrients are
absorbed through the villi. Each villus has an
epithelial cell covering whose free edge is covered
with microscopic folds called microvilli to further
increase the absorptive capabilities of the villus.
Each villus contains an arteriole, venule, capillary
network, and a lacteal that picks up fats.^
- The intestinal glands or crypts of Lieberkuhn secrete
the intestinal digestive enzymes. Brunner’s glands
secrete an alkaline mucus.^
- Chyme is the name of the digested contents of the
small intestine.
The Large Intestine
- The functions of the large intestine are the reab-
sorption of water, the manufacture and absorption of
certain vitamins, and the formation and expul-sion of
the feces.^
- The four regions of the large intestine are the ce-
cum, colon, rectum, and anus.
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- The colon is divided into the ascending colon,
transverse colon, and descending colon. It has
pouches or haustrae.^ - The rectum terminates at the anus. The anus is
controlled by an internal sphincter of smooth muscle
and an external sphincter of skeletal muscle.^ - The three mechanical movements that occur in the
large intestine are haustral churning, peristalsis at the
rate of 3 to 12 contractions per minute, and mass
peristalsis triggered by distention of the stomach.^ - Distention of the rectal walls initiates the defecation
reflex.
Review Questions
1.^ List the five basic activities of the digestive system.^
2. Name the major organs and the five accessory
-organs of the digestive tract.^
3.^ List the four walls or tunics of the digestive tract.^
4. Name the three pairs of salivary glands and discuss
why they are important for digestion.^
5. What are the three portions of a tooth and what
substance forms a tooth?^
6. Why is the pharynx considered essential to the
-process of swallowing?^
7.^ Name the four parts of the stomach.^
8. List the three types of secretory cells of the mucosa
of the stomach and what they secrete. Explain the
functions of those secretions.^
9. Name the two functions of the pancreas and
explain- what its secretions accomplish.^
10. Discuss why we cannot live without the liver.^
11. Name the three parts of the small intestine.^
12. List the two types of glands of the small intestine
and compare their function in the process of
digestion.^
13. Describe the anatomy and physiology of a typical
villus, including its function in the absorption of
nutrients.^
14. How does the large intestine contribute to the
digestive process?^
15. Name the four principal regions of the large
intestine.^
16. List the major digestive enzymes and how they
function.
Critical Thinking Questions